PROJECT SUMMARY Metastasis is the major cause of cancer mortality. Over 70% of all cancers metastasize to the bone, and the prognosis dramatically drops following bone metastasis. More than 350,000 Americans die every year due to bone metastasis. Colonization of the bone by the cancer cells leads to bone resorption, which results in microfractures from routine activities. Patients suffer debilitating pain, which decreases somatic, endocrine, and autonomic reflexes that further suppresses the immune system and accelerates metastasis. Currently, there is no effective treatment for bone metastasis. We propose to challenge this status quo by engineering the first bionanomaterial (Whitlockite)-based bone cement loaded with an immunotherapy drug for direct application to the bone. This is based on recent clinical evidences that show that the direct injection of polymethylmethacrylate (PMMA) bone cement at the metastatic osteolytic lesion can reduce pain by stabilizing microfracture. However, classical bone cements are not optimized for metastatic lesions, and suffer from major drawbacks. In contrast, Whitlockite (WH) nanoparticles are a major component of bone, are stable in the acidic metastatic niche, and can be used for drug delivery. In preliminary studies, we have already demonstrated that WH nanoparticle-based bone cements exhibit desirable properties for an ideal bone cement. In Aim.1. we will further identify the optimal structure of WH nanoparticles for formulating into a bone cement, and characterize the application of a WH nanoparticle-based bone cement for treating metastatic bone pain; in Aim 2. We will characterize WH nanoparticles as a drug-delivery platform. We will use immunotherapies that target the immune cells implicated in bone metastasis. We will rigorously test the pain-reducing efficacy, bone regeneration, and anti-metastatic effect of our immunomodulatory WH bone cement; in Aim 3, we will conduct a comprehensive toxicological test by analyzing stress response on bone and other organs to identify potential toxicities of using direct injection into the bone as a route of administration for nanoparticles. We envisage that this project will lead to fundamental insights into a novel nanomaterial (WH) and its application in drug delivery via a novel route (directly into bone lesion) of administration. The integration of immunotherapy with Whitlockite nanoparticles can lead to a paradigm shift in the treatment of bone metastasis, and directly impact a major unmet clinical need.